In recent years, vehicles such as a hybrid vehicle and an electric vehicle that are equipped with an electric motor as a power source have been improved to increase a capacity of a power storage unit for improving drive performance such as acceleration performance and a continuous travel distance. A structure having a plurality of power storage devices has been proposed as means for increasing the capacity of the power storage unit.
A Japanese Patent Laying-Open No. 2003-209969 has disclosed a power supply control system provided with a plurality of power supply stages. This power supply control system includes a plurality of power supply stages that are connected in parallel together and supply a DC power to at least one inverter. Each power supply stage includes a battery and a boost/buck DC-DC converter.
In this power supply control system, the plurality of power supply stages are controlled to maintain an output voltage for the inverter by uniformly charging and discharging a plurality of batteries that are included in the power supply stages, respectively.
Generally, in a power storage device such as a secondary battery and a capacitor, a capacity lowers with lowering of a temperature so that a charge/discharge property deteriorates with it. In the hybrid vehicle and others, therefore, the power storage device must be rapidly heated when the temperature of the power storage device is low. Particular, in system having a plurality of power storage devices such as the power supply control system disclosed in the above Japanese Patent Laying-Open No. 2003-209969, it is necessary to increase rapidly a temperature of the power storage device for sufficiently bringing out merits of the large capacity of power storage units.
However, the above Japanese Patent Laying-Open No. 2003-209969 has merely disclosed that the plurality of batteries included in the power supply stages respectively are uniformly charged and discharged in using the power storage device, and has not particularly disclosed a method for rapidly increasing a temperature of the plurality of power storage devices.
Further, from the viewpoint of cost and reliability, it is desired that a control circuit(s) or a quantity of control operation added for rapidly increasing a temperature of the plurality of power storage devices is as small as possible.